help with getline and sscanf

[c2tarun]

is it possible to read "P 6 5" using getline and separate 'P',6,5 in three variables one character and two integer using sscanf???
if yes please tell me how to do this.

[schauerlich]

Use fgets to read in a line, and strtok to split the line on each space.

[johnl]

#define _GNU_SOURCE /* for getline */
#include <stdlib.h>
#include <stdio.h>
#include <string.h>

int main(int argc, char* argv[])
{
size_t size = 128;
char* line = malloc(size);

ssize_t len = getline(&line, &size, stdin);
/* you should do some error checking on the
* return value of getline here. */

char c;
int i, j;

/* sscanf() returns the number of items successfully read */
if (sscanf(line, "%c %d %d", &c, &i, &j) != 3) {
printf("didn't get all three values\n");
} else {
printf("read %c, %d, and %d\n", c, i, j);
}

free(line);

return 0;
}

[trent.josephsen]

Use fgets to read in a line, and strtok to split the line on each space.
This. There's no reason to use a non-standard extension (getline) and a procedure for reading formatted strings (sscanf) to get input from the user. Problems like this are what strtok was made for.

[schauerlich]

The problem with using the scanf family is that when it fails, it can fail epically. It's much safer to read in a line at a time, and then parse it manually with strtok. This is especially easy with a simple example like this.

[johnl]

The problem with using the scanf family is that when it fails, it can fail epically. It's much safer to read in a line at a time, and then parse it manually with strtok. This is especially easy with a simple example like this.

I think in this case I would use fgets and then sscanf. There's no advantage to using strtok in this situation.

I would never use plain scanf to read user input. But could you provide an example of sscanf "failing epically?" I would rather use sscanf than mess around with tokenising and converting with strtok. Especially since there are some issues with strtok, such as (from the man page: )



* These functions modify their first argument.
* These functions cannot be used on constant strings.
* The identity of the delimiting character is lost.
* The strtok() function uses a static buffer while parsing, so it's not
thread safe. Use strtok_r() if this matters to you.


You can use strtok_r to avoid the last issue, but strtok_r is not part of the C standard like strtok.

[trent.josephsen]

The problem with sscanf in this situation is that you can't use it to read the input at all unless the input matches the format string exactly. If I

sscanf(line, "%c %d %d", &c, &i, &j);
and type "foo 2 3", it will fail, giving me no information as to what went wrong apart from the useless fact that 0 fields could be read. At this point I can either discard the input entirely, as scanf does, or else fall back on using strtok or a similar method, which I should have done in the first place.

In a nutshell, scanf and friends simply do not give enough information. It makes sense to use them only when you know the format of the input and don't care about input that is not in that format. In some cases, it's acceptable to say "I didn't understand that line; therefore, I'm going to ignore it entirely". Interactive user input is not one of those cases.

[c2tarun]

thanx a lot evryone.:)